Copper interconnect by immersion/electroless plating in dual damascene process

ABSTRACT

The invention is directed to a fabrication method of copper interconnects using dual damascene processing. Using silicon to provide an active surface, palladium can be selectively deposited on silicon by immersion plating technique. After palladium deposition (about 1000 A thick), either a layer of cobalt phosphorus or alloy cobalt/nickel phosphorus or nickel phosphorus is deposited on palladium layer using electroless plating technique. This cobalt/phosphorus, cobalt nickel phosphorus alloy, or nickel phosphorus layer serves as a copper diffusion barrier. Via and trench are filled up by copper from electroless copper plating method and CMP is used to remove excess copper and planarize/polish the copper/dielectric surface.

BACKGROUND

[0001] In the manufacture of devices on a semiconductor wafer, it is now the practice to fabricate multiple levels of conductive (typically metal) layers above a substrate. The multiple metallization layers are employed in order to accommodate higher densities as device dimensions shrink well below one micron design rules. Thus, semiconductor “chips” having three and four levels of metallization are becoming more prevalent as device geometries shrink to sub-micron levels.

[0002] One common metal used for forming metal lines (also referred to as wiring) on a wafer is aluminum. Aluminum is used because it is relatively inexpensive compared to other conductive materials, it has low resistivity and is also relatively easy to etch. Aluminum is also used as a material for forming interconnections in vias to connect the different metal layers. However, as the size of via/contact holes is scaled down to a sub-micron region, the step coverage problem appears, which has led to reliability problems when using aluminum to form the interconnection between different wiring layers. The poor step coverage in the sub-micron via/contact holes result in high current density and enhance the electromigration.

[0003] One material which has received considerable attention as a replacement material for VLSI interconnect metallizations is copper. Since copper has higher resistance to electromigration and lower resistivity than aluminum, it is a more preferred material for interconnect (plugs and wiring) formation than aluminum. However, one serious disadvantage of using copper metallization is that it is difficult to etch. Thus, where it was relatively easier to etch aluminum after deposition to form wiring lines or plugs (both wiring and plugs are referred to as interconnects), substantial additional cost and time are now required to etch copper.

[0004] One typical practice in the art is to fabricate copper plugs and wiring by inlaid (Damascene) structures by employing CMP. Dual Damascene processing eliminates not only the need for metal etch (which is increasingly challenging in aluminum interconnects and nearly impossible with copper), but also the need for dielectric gap fill (another challenging process). This technique involves the creation of interconnect lines by first etching a trench or canal in a planar dielectric layer, and then filling that trench with metal, such as aluminum or copper. In dual damascene processing, a second level is involved where a series of holes (i.e., contacts or vias) are etched and filled in addition to the trench. After filling, the metal and dielectric are planarized by chemical-mechanical polishing (CMP). The challenge associated with copper interconnect is how to deposit a thin layer of material on the trench and via as diffusion barrier to prevent copper diffusion. The trick is to keep the diffusion barrier thin so that it does not negatively impact the resistivity of the plug, while still acting as a good barrier to diffusion. A variety of techniques have been developed to deposit copper, including chemical vapor deposition (CVD), plasma vapour deposition (PVD), sputtering, electroplating, and electroless plating. After copper deposition, a chemical mechanical polishing (CMP) process is used to planarize/polish the metal/dielectric surface.

SUMMARY

[0005] The invention is directed to a fabrication method of copper interconnects using dual damascene processing. Using silicon or polysilicon to provide an active surface, palladium can be selectively deposited on silicon by immersion plating technique. After palladium deposition (about 1000 A thick), either a layer of cobalt phosphorus or alloy cobalt/nickel phosphorus or nickel phosphorus is deposited on palladium layer using electroless plating technique. This cobalt/phosphorus, cobalt nickel phosphorus alloy, or nickel phosphorus layer serves as a copper diffusion barrier. Via and trench are filled up by copper from electroless copper plating method and CMP is used to remove excess copper and planarize/polish the copper/dielectric surface.

[0006] These together with other objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects obtained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention.

DESCRIPTION OF THE DRAWING

[0007]FIGS. 1 through 9 are schematic illustrations of side elevation views of layers of a wafer fabricated in accordance with the process of the present invention.

DETAILED DESCRIPTION

[0008] This invention describes a fabrication method of copper interconnects using dual damascene processing. Using doped amorphous silicon or polysilicon to provide an active surface, palladium can be selectively deposited on silicon by immersion plating techniques. This novel deposition technique was described in U.S. Pat. No. 5,358,907 entitled “Method of Electrolessly Depositing Metals on a Silicon Substrate By Immersing the Substrate in Hydrofluoric Acid Containing a Buffered Metal Salt Solution “by Kaiser Wong. After palladium deposition (about 1000 A thick), either a layer of cobalt phosphorus or alloy cobalt/nickel phosphorus or nickel phosphorus is deposited on palladium layer using electroless plating technique. This cobalt/phosphorus, cobalt nickel phosphorus alloy, or nickel phosphorus layer serves as a copper diffusion barrier. Via and trench are filled up by copper from electroless copper plating method and CMP is used to remove excess copper and planarize/polish the copper/dielectric surface. This fabrication process is illustrated and more fully described below with reference to FIGS. 1 to 9.

[0009] Reference is now made to FIG. 1 wherein there is shown a metal coated semiconductor wafer comprising a semiconductor silicon substrate 48 having a layer of silicon oxide 22. To make the metal conductor 20 a trench is formed by depositing layers of a copper diffusion barrier consisting of silicon 42, palladium 44 and palladium immersion/cobalt, or cobalt/nickel, or nickel electroless plating/copper 40 plating in the trench as shown in FIG. 1. FIG. 2 shows the encapsulating material 24 consisting palladium 44 and palladium immersion/cobalt, or cobalt/nickel, or nickel electroless plating/copper 40 coated with silicon or polysilicon 22 and CMP is used to planarize the surface.

[0010] Referring once again to FIG. 2, insulator layer (silicon oxide) 22 with silicon nitride 26, acting as an etch stop is deposited wherein a photoresist pattern 30 is next deposited, on the wafer of FIG. 1. Next, the exposed silicon nitride is etched away and the photoresist is stripped to form the via pattern 32 and a silicon oxide 22 insulator is deposited, as shown in FIGS. 3 and 4. As shown in FIG. 5 a pattern photoresist 30 is deposited for forming the interconnect trenches. Next, the silicon oxide layer 22 is etched (according to the photoresist pattern) to form the trenches 34 and vias 32 and with the remaining photoresist stripped away as shown in FIG. 6.

[0011] Referring now to FIG. 7, a thin layer (1000 A) of doped amorphous or polysilicon 42 is deposited by chemical vapor deposition (CVD) followed by immersion palladium (1000 A) 40 and cobalt(p), or cobalt/nickel(p), or nickel (p)(1000 A) electroless plating. Copper 34 is next deposited to fill up the vias 32 and trenches 34 by electroless copper plating, as shown in FIG. 8. Lastly, using Chemical Mechanical Polishing (CMP) excess copper 34 and palladium/cobalt phosphorous or nickel (p) and doped amorphous or polysilicon 42 is removed and planarize copper/oxide surface. The above process may be repeated for multilayer interconnection.

[0012] It should be noted that after annealing at 400 C the amount of the interdiffused copper into 1000 A thick Co(P), or Co/Ni (P), or Ni (P) is less than 1 atomic percentage. The contact resistivity is in the 10⁻⁸ ohms range for Ni(P)(reference). Pd₂Si (palladium silicide) is formed during thermal treatment. There is also observed low contact resistance of the Pd₂Si/Si junction. The copper obtained from electroless plating has an electrical resistivity of about 1.8 uohms cm, much lower than 2.5 u ohms cm of resistivity of aluminum.

[0013] This invention proposes a method of fabricating copper interconnect in VLSI and ULSI metallization. It is appealing because of the low cost of the equipment and materials and the high throughput of the process. Immersion and electroless plating techniques employed in this invention are highly selective, depositing the desired metallization to the desired patterns. They have excellent step coverage and good via/trench filling capability.

[0014] It should further be noted that numerous changes in details of construction and the combination and arrangement of elements may be resorted to without departing from the true spirit and scope of the invention as hereinafter claimed. 

What is claimed is:
 1. A fabrication method of copper interconnects using dual damascene processing, comprising: providing doped amorphous silicon or polysilicon as an active surface; selectively depositing palladium on the silicon by immersion plating technique; depositing a layer of cobalt phosphorus or alloy cobalt/nickel phosphorus or nickel phosphorus on the palladium layer using electroless plating technique; cobalt/phosphorus, cobalt nickel phosphorus alloy, or nickel phosphorus layer serves as a copper diffusion barrier; filling up via and trench by copper from electroless copper plating; and removing excess copper and planarize/polish the copper/dielectric surface.
 2. The fabrication method of copper interconnects according to claim 1, further comprising: depositing a photoresist pattern and etching away any exposed silicon nitride.
 3. The fabrication method of copper interconnects according to claim 2, further comprising: stripping the photoresist form the via patterns.
 4. The fabrication method of copper interconnects according to claim 3, further comprising: stripping the photoresist to form via patterns.
 5. The fabrication method of copper interconnects according to claim 4, further comprising: depositing a silicon oxide layer to form an insulator.
 6. The fabrication method of copper interconnects according to claim 5, further comprising: depositing a pattern photoresist for defining interconnect trenches.
 7. The fabrication method of copper interconnects according to claim 6, further comprising: etching the silicon oxide layer is etched according to the photoresist pattern to form the trenches and vias and stripping away the remaining photoresist.
 8. The fabrication method of copper interconnects according to claim 7, further comprising: depositing a thin layer (1000 A) of doped amorphous or polysilicon is by chemical vapor deposition (CVD).
 9. The fabrication method of copper interconnects according to claim 8, further comprising: depositing palladium (1000 A) and cobalt(p), or cobalt/nickel(p), or nickel (p)(1000 A) by electroless plating.
 10. The fabrication method of copper interconnects according to claim 9, further comprising: depositing copper to fill up the vias and trenches by electroless copper plating.
 11. The fabrication method of copper interconnects according to claim 10, further comprising: removing excess copper and palladium/cobalt phosphorous or nickel (p) and doped amorphous or polysilicon using Chemical Mechanical Polishing (CMP) and planarize copper/oxide surface.
 12. The fabrication method of copper interconnects according to claim 11, further comprising: annealing at 400 C an amount of interdiffused copper into 1000 A thick Co(P), or Co/Ni (P), or Ni (P) is less than 1 atomic percentage.
 13. The fabrication method of copper interconnects according to claim 12, further comprising: forming Pd₂Si (palladium silicide) during thermal treatment with a contact resistivity is in the 10⁻⁸ ohms range for Ni(P).
 14. A fabrication method of copper interconnects using dual damascene processing, comprising: providing doped amorphous silicon or polysilicon as an active surface; selectively depositing palladium on the silicon by immersion plating technique; depositing a layer of cobalt phosphorus or alloy cobalt/nickel phosphorus or nickel phosphorus on the palladium layer using electroless plating technique; cobalt/phosphorus, cobalt nickel phosphorus alloy, or nickel phosphorus layer serves as a copper diffusion barrier; filling up via and trench by copper from electroless copper plating; removing excess copper and planarize/polish the copper/dielectric surface; depositing a photoresist pattern and etching away any exposed silicon nitride; stripping the photoresist form the via patterns; stripping the photoresist to form via patterns; and depositing a silicon oxide layer to form an insulator.
 15. The fabrication method of copper interconnects according to claim 14, further comprising: depositing a pattern photoresist for defining interconnect trenches.
 16. The fabrication method of copper interconnects according to claim 15, further comprising: etching the silicon oxide layer is etched according to the photoresist pattern to form the trenches and vias and stripping away the remaining photoresist.
 17. The fabrication method of copper interconnects according to claim 16, further comprising: depositing a thin layer (1000 A) of doped amorphous or polysilicon is by chemical vapor deposition (CVD).
 18. The fabrication method of copper interconnects according to claim 8, further comprising: depositing palladium (1000 A) and cobalt(p), or cobalt/nickel(p), or nickel (p)(1000 A) by electroless plating.
 19. The fabrication method of copper interconnects according to claim 18, further comprising: annealing at 400 C an amount of interdiffused copper into 1000 A thick Co(P), or Co/Ni (P), or Ni (P) is less than 1 atomic percentage.
 20. A fabrication method of copper interconnects using dual damascene processing, comprising: providing doped amorphous silicon or polysilicon as an active surface; selectively depositing palladium on the silicon by immersion plating technique; depositing a layer of cobalt phosphorus or alloy cobalt/nickel phosphorus or nickel phosphorus on the palladium layer using electroless plating technique; cobalt/phosphorus, cobalt nickel phosphorus alloy, or nickel phosphorus layer serves as a copper diffusion barrier; filling up via and trench by copper from electroless copper plating; removing excess copper and planarize/polish the copper/dielectric surface; depositing a photoresist pattern and etching away any exposed silicon nitride; stripping the photoresist form the via patterns; stripping the photoresist to form via patterns; depositing a silicon oxide layer to form an insulator; depositing a pattern photoresist for defining interconnect trenches; etching the silicon oxide layer is etched according to the photoresist pattern to form the trenches and vias and stripping away the remaining photoresist; depositing a thin layer (1000 A) of doped amorphous or polysilicon is by chemical vapor deposition (CVD); and depositing palladium (1000 A) and cobalt(p), or cobalt/nickel(p), or nickel (p)(1000 A) by electroless plating. 